Jellyfish robot teaches scientists something new about propulsion

Researchers working on a Navy-funded study to develop a jellyfish-inspired robot have discovered something key to marine animal propulsion in the water. Scientists love to look to nature for inspiration for technology. Animals do things efficiently and with an agileness that our robots aren't capable of yet. By studying the secrets of their movements and trying to copy that, technological breakthroughs can be found.

The robotic jellyfish are no different. The Navy has sponsored a national program to make underwater robots that move with the ease of jellyfish, but while researchers were trying to improve the robot, they found that something that increased the efficiency of the robot's movements was something used by many flying and swimming animals -- a way of bending the tips of wings, fins, flukes, mollusk feet, and other propulsors across many animal species from fruit flies to whales.

The researchers had outfitted the robo-jellyfish with a passive, flexible, silicone margin around the jellyfish bell that providing that bending action and propulsive proficiency improved by orders of magnitude. They then studied videos of 59 animals in steady motion (not accelerating or decelerating) and found that all the animals' propulsors bent in a similar way at the tip while repeating a predictable range of movements.

Evolutionarily this means big things.

"We found that the way the propulsors moved—the kinematics—seems to be selected for across this wide range of animals, rather than the material properties, such as feathers or scales, being key," said John H. Costello of Providence College and the Marine Biological Laboratory (MBL) in Woods Hole. "Discovering these uniform bending characteristics has reoriented our search for understanding the advantages of flexibility in propulsion."

Armed with this information, scientists will be able to create better underwater vehicles in the future, ones that come closer to moving as efficiently and nimbly through the water as their natural counterparts.

"Flying and swimming animals have a much lower cost of transport (energy needed to move a mass a given distance) than present manmade designs of similar scale," Costello says. "That is part of our motivation for understanding biological design: Animals do it better."